[Talk-us] City boundaries on the Canada/US border

Alexander Roalter alexander at roalter.it
Fri Mar 30 13:18:27 BST 2012

Am 30.03.2012 11:17, schrieb Paul Norman:
> There are a significant number of cities in BC and Washington which have
> borders that in practice[1] coincide with the Canada/US border. Currently in
> OSM these are represented with many nearly-overlapping ways.
> The Canada/US border here consists of the BC-WA border, BC-ID border, BC-MT
> border, AB-MT border, SK-MT border, SK-ND border, etc. There are separate
> ways for the cities on the Canada side and cities on the US side.
> This would reduce the number of ways present when you download a section of
> the border and have many advantages. The one big disadvantage is that it
> would boost the number of ways in the Canada and US relations. This
> increases the chance of conflicts and also increases the number of places it
> could be broken.

I merged the us/canadian border with the north dakota, minnesota and 
montana state borders and also county borders a while ago, and I agree 
that there should only be one way for one part of the border, this line 
being shared in all affected boundary relations.
I don't really think this will increase conflicts, as if you delete one 
way of a border, all affected relations will be notified (at least in 
JOSM it's impossible to download a way without downloading all relations 
this way is connected.

I did include city boundaries where available, but this was the case 
only on one city (Emerson, MB). In Europe, nearly all borders are made 
up of individual municipality border stretches (I once loaded italy's 
circumference, made up of >2500 ways).

> Either way, the Canada/US border will remain very complex with so many
> different boundary relations ending there.
> If I do this, I will also align the borders to the IBC data (PD). I've
> investigated the accuracy of their data, and it agrees with the markers on
> the ground to within 10cm. I believe the most significant source of error in
> their data is the NAD83 to WGS84 conversion.
> [1]: The actual legal situation is much more complicated and serves as a
> good example of the problems that arise when you define what is supposed to
> be one line in multiple ways. The biggest oddity is that the Washington
> border extends out of the United States into Canada. All of the other
> oddities are just a few meters at most.


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